Optical fiber connectors are an essential part of substantially any optical fiber communication system. For instance, such connectors may be used to join segments of fiber into longer lengths; to connect fiber to active devices such as radiation sources, detectors and repeaters; or to connect fiber to passive devices such as switches and attenuators. The central function of an optical fiber connector is the maintenance of two optical fiber ends such that the core of one of the fibers is axially aligned with the core of the other fiber. When the ends are aligned properly, there will be little or no connection loss due to core misalignment.
However, not all of the loss in an optical fiber connection is attributable to core misalignment. Sharp bends in the optical fiber itself cause substantial loss in a lightwave signal, particularly at long wavelengths (1550 nanometers) now being used for the highest data transmission speeds. When the optical fiber is bent in a curved path, the smaller the bend radius, the greater the path loss. This is especially true for matched-clad, singlemode fiber (as compared to depressed-clad, singlemode fiber). However, if the bend radius is sufficiently large, then path loss is not a concern. Bending occurs during cable placement and occasionally occurs when the cable, which contains the optical fiber, is routed around a sharp corner or becomes "kinked" due to handling. More frequently, sharp bends occur in the region where the connector is plugged into a panel, and its attached cable needs to be bent (usually by 90.degree.) to be routed to its destination. Indeed, such panels are frequently equipped with access doors which, when closed, press against the back portion of the connector and cause its associated cable to bend sharply. Such bending also occurs when a jumper (comprising an optical cable and a connector) is inserted into a receptacle and the cable is pulled in a direction which is perpendicular to the central axis of the connector. The sharp bend at the junction where the cable attaches to the connector causes excessive transmission loss in the lightwave signal.
Strain-relief boots are well-known devices for transferring axial tension from the cable to the connector, and they also function to limit the amount of bending that can occur at the junction where the cable is joined to the connector. Such boots are generally cylindrical and surround the optical cable at the cable/connector junction. The diameter of the boot is approximately equal to the diameter of connector where they meet, and it tapers to the diameter of the cable where the cable enters the boot. One popular design of a strain-relief boot includes a number of bend-limiting segments which are separated from each other by a gap that is approximately equal to the width of each segment. When the cable is bent, the segment portions on the inside of the bend come closer together until they finally touch, thereby limiting the minimum radius of the bend. While such designs provide acceptable results over a narrow range of side loads, they have not been completely successful over side loads that range, for example, from 0.5 to 10 pounds. Nevertheless, such wide ranges are routinely encountered during normal handling. Depending on the material used for the bend-limiting boot, and its pattern of segments, sharp bending will either occur at the junction where the cable meets the boot (light load), or sharp bending will occur at the junction where the boot meets the connector (heavy load). In either event, excessive transmission loss will be experienced by lightwave signals traveling within the optical cable when the bend is too sharp.
It is noted that bend-limiting boots can be designed to handle a very wide range of side loads if the dimensions of the boot are unconstrained. For example, a cone-shaped boot having a large diameter at one end, a narrow diameter at the other end, and a very long distance between these ends can be designed to satisfy virtually any load range. However, as a practical matter, the size (diameter) of the bend-limiting boot should be approximately equal to the size of the connector where they join together, and the boot cannot be too long. Seemingly, the prior art has not provided a bend-limiting boot for use with optical connectors which is compact and yet capable of handling a wide range of side loads.